Heretofore, a so-called radiation method which applies a silver salt to obtain a radiation image has been utilized, while a method to convert a radiation image into a visual image without using a silver salt has been developed. That is, developed has been a method in which radiation, which passed through a photographic object, is absorbed by a stimulable phosphor substance, thereafter this stimulable phosphor substance is excited with a certain type of energy to make radiation energy accumulated in this stimulable phosphor substance be emitted as fluorescent light, which is detected to be made into an visual image.
As a specific method, for example, as described in U.S. Pat. No. 3,859,527, known is a radiation image storage method in which a panel provided with a stimulable phosphor substance layer is utilized and either one of or both of visual rays and infrared rays are employed as excitation energy.
In recent years, as a radiation image storage method utilizing a stimulable phosphor substance provided with high luminance, high sensitivity and high sharpness, proposed has been a radiation image storage panel utilizing a stimulable phosphor substance comprising an alkali halogenide such as CsBr as a mother material being activated by Eu. It is said that improvement of an efficiency of an X-ray conversion ratio, which has been conventionally impossible, becomes possible.
Further, a radiation image storage panel having a higher sharpness has been required in analysis of diagnostic images, and as a means to improve sharpness, for example, an attempt to improve sensitivity and sharpness by controlling a configuration of a stimulable phosphor substance itself, has been made.
As one of these attempts, for example, as described in JP-A No. 2-58000 (hereinafter, JP-A refers to Japanese Patent Publication Open to Public Inspection), proposed has been a radiation image conversion panel which is provided with a stimulable phosphor substance layer comprising slender columnar crystals having a certain slope against the normal direction of a support.